Non-destructive ultrasonic flaw inspection is a well developed art and numerous devices have been designed for this purpose. Some examples of such ultrasonic inspection devices are those disclosed in U.S. Pat. Nos. 3,350,923 (Cross); 3,745,813 (Uozumi); 3,763,694 (Rathburn et al) and 3,798,961 (Flambard et al).
A serious problem associated with most conventional ultrasonic inspection devices is that these devices require a smooth test surface in order to be effective. In fact, it is understood that one of the basic requirements in all military specifications and codes is that ultrasonic tests shall be performed on smooth surfaces. This limitation presents obvious difficulties in attempting to locate material flaws in regions of maximum thermal stress in test objects having threaded holes therein in that the maximum thermal stress regions are located adjacent to the threaded holes and cannot be reached using conventional methods which require smooth surfaces to carry out the ultrasonic inspection.